Digital television system

ABSTRACT

Disclosed is a digital television system carrying out modulation/demodulation by VSB (vestigial side band). A VSB transmitter includes an additional error correction encoder designed in a manner that a signal mapping of a TCM encoder is considered, a multiplexer (MUX), a TCM encoder operating in a manner corresponding to state transition processes of the additional error correction encoder, and a signal transmission part including an RF converter. And, A VSB receiver includes a signal receiver part receiving a signal transmitted from the transmitter, a TCM decoder, a signal processing part including a derandomizer, and an additional error correction decoder part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/962,263, filed Sep. 26, 2001, now abandoned, which claims the benefitof earlier filing date and right of priority to Korean PatentApplication No. 10-2000-56473 filed on Sep. 26, 2000, the contents ofwhich are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital television system carryingout modulation/demodulation by VSB (vestigial side band).

2. Background of the Related Art

An 8VSB transmission system for terrestrial wave digital broadcasting istaken as a U.S. standard system in 1995 is test-broadcasted from thelatter half of the year 1998. Such a test broadcasting using aterrestrial wave digital broadcasting standard based on the U.S.standard system is being carried out in Korea as well.

In such a digital broadcasting system, a transmitted signal is receivedby a receiver through a terrestrial channel. In order to restore thesignal in the receiver despite the noise caused by the channel, thesignal is variously coded to be transmitted. In response to the variouscoding process, the receiver carries out the corresponding decodingprocess so as to restore the transmitted signal.

Lately, a broadcasting station tries to transfer such a digitalbroadcasting, which transfers mainly audio and video data, to whichvarious additional data are attached. The additional data includesstock-market information, weather casting, program guide information,HTML, execution files and the like.

FIG. 3 illustrates a structural diagram of a Trellis Coded Modulation(TCM) encoder according to a related art.

Referring to FIG. 3, a TCM encoder includes a precoder 1 outputting afirst output signal by precoding a first input bit d1 and an encoderoutputting a third output signal by encoding a second input bit as asecond output signal c1, where a reference numeral ‘3’ indicates a 8VSBmapper.

Meantime, the precoder 1 includes an adder 1 a outputting the firstoutput signal c2 by adding the first input bit d1 to a delayed signaland a memory 1 b providing the adder 1 a with the delayed signalattained by delaying an output signal of the adder 1 a.

The TCM encoder according to a related art may cause a fatal damage onthe additional data when using it.

Different from general audio/video data in channel transmission, theadditional data is vulnerable fatally to an influence of the channelnoise. For example, the damaged additional data of which informationitself is defected may inform a viewer with wrong information, while thedamaged general audio/video data just result in light image/voice loss.

Specifically, when the additional data include numbers or an executionfile, a minor data error causes a devastating result of failing theentire operation.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a digital televisionsystem that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a digital televisionsystem fitting for transmitting additional data.

Another object of the present invention is to provide a digitaltelevision system robust to a noise.

A further object of the present invention is to provide a digitaltelevision system compatible with a conventional digital televisionsystem.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, aVSB transmitter includes an additional error correction encoder carryingout state transition processes on additional data inputted to correct anerror and designed for a TCM coding to be considered wherein the TCMcoding will be carried out later, a multiplexer multiplexing theadditional data and Advanced Television Systems Committee (ATSC) datawherein the additional and ATSC data are inputted thereto, a TCM encoderoperating in a manner corresponding to the state transition processes ofthe additional error correction encoder and encoding the ATSC andadditional data outputted from the multiplexer, and a signaltransmission part converting the ATSC and additional data outputted fromthe TCM encoder into an RF (radio frequency) signal and transmitting theRF signal to a receiver.

In another aspect of the present invention, a VSB receiver includes anRF tuner tuning RF signal transmitted from a VSB transmitter, a VSBdemodulator demodulating IF signal outputted from the RF tuner, a TCMdecoder decoding the ATSC data and additional data, a deinterleaverdeinterleaving soft output of the TCM decoder, a limiter carrying out ahard decision on the soft-outputted ATSC data, an RS decoder decodingthe hard-outputted ATSC data, a derandomizer derandomizing the ATSC datahaving passed through the RS decoder, and an additional error correctiondecoder part carrying out an error correction on the soft-outputtedadditional data.

Preferably, the TCM decoder in the VSB receiver is a decoder producing asoft output signal with a soft input signal.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a TCM encoder and a signal mapper in an ATSC 8VSBsystem according to a related art;

FIG. 2 illustrates a diagram for a set partitioning used in the TCMencoder in FIG. 1;

FIG. 3 illustrates a structural diagram of a TCM encoder according to arelated art;

FIG. 4 illustrates a performance graph of a TCM encoder in an 8VSBsystem on an AWGN(additive white Gaussian noise) channel;

FIG. 5 illustrates a VSB communication system according to the presentinvention;

FIG. 6 illustrates a VSB transmitter according to the present invention;

FIG. 7 illustrates a TCM encoder according to the present invention; and

FIG. 8 illustrates a VSB receiver according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 4 illustrates a performance graph of a TCM code of an 8VSB systemin AWGN(additive white Gaussian noise) channel.

A bit error rate of an uncoded bit d1, another bit error rate of a codedbit d0, and a total bit error rate when regarding the uncoded and codedbits d1 and d0 as one stream are shown in FIG. 4.

Referring to FIG. 4, the bit error rate of the uncoded bit is lower thanthat of the coded bit. And, the bit error rate of the entire bitscorresponds to an average between the respective bit error rates of theuncoded and coded bits. It is because a sub-set is determined by thecoded bit, while a signal in the determined sub-set is determined by theuncoded bit.

When a set partitioning of the TCM code, a performance of the uncodedbit determining signals in the sub-set is superior to that of the codedbit since a distance between signals in one sub-set is allotted so as tobe longer than that that between signals two different subsets.

In use of such a characteristic, data having a higher significance areinputted using the uncoded bit d1 having a relatively lower bit errorrate than the coded bit d0 and another data having a less significanceare inputted using the coded bit c0 having a higher bit error rate thanthe uncoded bit d1. Therefore, it is able to design a more efficientdigital television system.

FIG. 5 illustrates a VSB communication system according to the presentinvention.

Referring to FIG. 5, the VSB communication system is divided into a VSBtransmitter and a VSB receiver.

The VSB transmitter is constructed with an additional error correctionencoder 10 encoding additional data to correct an error thereofadditionally and designed in a manner that a signal mapping of a TCMencoder is considered, a multiplexer(MUX) 20 multiplexing an outputsignal of the additional error correction encoder 10 and inputted ATSCdata, a TCM encoder 30 operating in a manner corresponding to statetransition processes of the additional error correction encoder 10, anda signal transmission part 40 transmitting an output of the TCM encoder30 as a radio base to a receiver side.

The VSB receiver is constructed with a signal receiver part 50 receivinga signal transmitted from the signal transmission part 40, i.e. atransmitter side, a TCM decoder 60 decoding a signal outputted from thesignal receiver part 50, a signal processing part 70 processing anoutput signal of the TCM decoder 60, and an additional error correctiondecoder 80 restoring the additional data by decoding the output signalof the TCM decoder 60 additionally.

The signal processing part 70 is constructed with a limiter limiting theoutput signal of the TCM decoder 60, an RS decoder decoding an outputsignal of the limiter, and a derandomizer derandomizing an output signalof the RS decoder.

FIG. 6 illustrates a VSB transmitter according to the present invention.

Referring to FIG. 6, a VSB transmitter is constructed with an additionalerror correction encoder 110 carrying out an encoding for correcting anerror additionally on additional data, a multipluxer(MUX) 120multiplexing the additional data and the general ATSC data failing topass through the additional error correction encoder 110, a randomizer130 randomizing an output signal of the multiplexer 120, anRS(reed-solomon) encoder 140 RS-encoding an output signal of therandomizer 130 to add a parity code, an interleaver 150 interleaving anoutput signal of the RS encoder 140 to protect transmission data from aburst noise possibly occurring on a transmission channel, a TCM encoder160 encoding an output signal of the interleaver 150 into a TCM code, aVSB modulator 170 VSB-modulating an output signal of the TCM encoder160, an RF converter 180 converting an output signal of the VSBmodulator 170 into an RF signal, and a transmission antenna 190transmitting the RF signal to a receiver side.

FIG. 7 illustrates a detailed construction of the TCM encoder 160 inFIG. 6 according to the present invention, where the TCM encoder 160 istransformed from a conventional precoder.

Referring to FIG. 7, a TCM encoder is constructed with a precoder 161outputting a second switch input signal s1 by preceding a first inputbit d1 as a first switch input signal s0, an inverter 162 outputting athird switch input signal s2 by inverting the second switch input signals1, a comparator 163 providing a switching control signal by comparingthe first and second switch input signals s0 and s1 each other, a switch164 selectively outputting one of the first to third switch inputsignals s0 to s2 as a first output signal c2, and an encoder 165encoding a second input bit d0 as a second output signal c1 so as tooutput a third output signal c0. And, a reference numeral ‘166’indicates a VSB mapper.

When the first input bit d1 is additional data, the input bit d1 isoutput through the switch s0. At this time, the input bit d1 is alsoinput to the precoder 161. When the first input bit d1 is ATSC data, theinput bit d1 is divided into two depending on the last bit of theadditional data. If the output of the switch s0 at the last bit is equalto the output of the switch s1, an output value of the precoder isoutput, If not so, an inverse value of the precoder is output.

Meanwhile, the precoder 161 includes an adder 161 a outputting thesecond switch input signal s1 by adding the first input bit d1 and adelayed signal each other and a memory 161 b providing the adder 161 awith a signal attained by delaying an output signal of the adder 161 afor a predetermined time.

The above operations on the first bit d1 is to bypass the precoder incase of additional symbol and maintain compatibility with the relatedart VSB receiver. The term “compatibility” means that even though theprecoder is bypassed in case of additional symbol, the related art VSBreceiver can decode ATSC data symbol without error.

The operation of the VSB transmitter is explained in detail as follows.

Different from the general ATSC data, the additional data for additionalservices such as an execution file, HTML and the like require theadditional error correction encoder 110 for preventing a performancedegradation caused by the noise.

First, for error correction, the additional data having passed throughthe additional error correction encoder 110 and the general ATSC datafailing to pass through the additional error correction encoder 110 aremultiplexed by the multiplexer 120 so that one of the additional andATSC data is outputted.

Subsequently, the additional or ATSC data passed through the multiplexer120 enter the randomizer 130.

In this case, the additional data bypasses the randomizer 130, while theATSC data becomes random through the randomizer 130.

A parity is then added to the additional data and the ATSC data passedthrough the randomizer 130 in the RS(reed-solomon) encoder 140. And, theadditional and ATSC data are interleaved in the interleaver 150 so as toprotect the transmission data from the burst noise might occur in thetransmission channel.

Then, the additional and ATSC data outputted from the interleaver 150are encoded again in the TCM encoder 160.

As mentioned in the above explanation, the additional and ATSC datapassed through the TCM encoder 160 are free from errors even if theadditional data are inputted thereto, which is different from the caseusing the conventional precoder failing to have the switching functionin FIG. 3.

For instance, let's assume that a bit 0 is put in the memory 1 b of theprecoder 161 in FIG. 3 and that a bit stream inputted into the precoderis the following a1.1011001000010111011001  (a1),where underlines beneath the stream a1 indicates an additional datainterval which is additional-error-correction-encoded.

When the additional data interval of the bit stream a1 fails to passthrough the precoder 161 and the ATSC code interval passes through theprecoder 161, the following bit stream a2 is attained.110110100011011011001  (a2)

If all of the bit stream a2 pass through a post decoder, an output ofthe post decoder is represented by the following bit stream a3.101101110010110110101  (a3)

In the bit stream a3, a bit 1 denoted by a bold(darkened) numeral of 1belongs to the previous ATSC data interval, which means that an erroroccurs. Namely, comparing the input bit stream a1 to the output bitstream a3 of the post decoder, the darkened bit of the output bit streama3 of the post decoder is changed in the previous ATSC data intervalexcluding the additional data interval(the underlined bits).

However, after the input bit stream a1 passes through the TCM encoder160 corresponding to the modified precoder in FIG. 7, the followingstream a4 shows up.110110100011011011110  (a4)

After all of the bit stream a4 pass through the post decoder, the postdecoder outputs the following bit stream a5.101101110010110110001  (a5)

Hence, after the input stream a1 having passed through the modifiedpredecoder passes the post decoder, the bit stream a5 outputted from thepost decoder becomes equal to the input bit stream a1 in the previousATSC data interval. Namely, no bit stream error takes place in theprevious ATSC data interval.

FIG. 8 illustrates a diagram of a VSB receiver according to the presentinvention.

Referring to FIG. 8, the VSB receiver is constructed with an RF(radiofrequency) tuner tuning the RF signal received through an antenna 200, aVSB demodulator 220 demodulating IF signal outputted from the RF tuner210, a TCM decoder 230 decoding an output signal of the VSB demodulator220 and then providing soft output, a deinterleaver 240 deinterleavingthe ATSC and additional data having the soft signal form outputted fromthe TCM decoder 230, a demultiplexer 250 dividing the data outputtedfrom the deinterleaver 240 into the additional data and the ATSC dataand then outputting the divided data, a limiter 260 deciding the ATSCdata outputted from the demultiplexer 250, an RS decoder 270 decoding anoutput signal of the limiter 260, a derandomizer 280 derandomizing anoutput signal of the RS decoder 270, an RS parity removal part 290removing a parity from the additional data outputted from thedemultiplexer 250, and an additional error correction decoder part 300decoding an output signal of the RS parity removal part 290 for errorcorrection.

Operation of the VSB receiver is explained as follows.

First, the additional and ATSC data received from the VSB transmitterthrough the antenna 200 are tuned through the RF tuner 210.

The ATSC and additional data outputted from the RF tuner 220 aredemodulated through the VSB demodulator 220. the output signal of theVSB demodulator 220 is decoded by the TCM decoder 230 so as to beoutputted as the soft signal form.

At this moment, the TCM decoder 230 should produce a soft output inorder to maximize a performance of the additional error correctionencoder 110 in the transmitter shown in FIG. 6.

SOVA(soft output viterbi algorithm) and MAP(maximum A posteriori) arealgorithms for producing a soft output for a trellis coded data. Inaspect of a symbolic error, the MAP algorithm is superior to SOVA.

However, the optimal MAP algorithm has disadvantages such as acalculation of probability in an exponential domain and a presumption ofa noise variance of a transmission channel.

Besides, there is SSA(suboptimum soft output algorithm) as a sort of theMAP algorithm, in which a probability is calculated in a logarithmicdomain without reducing a performance of the receiver and thepresumption of the noise variance is unnecessary.

Therefore, if the SSA algorithm is used as a decoding algorithm, foursoft outputs, which are shown in the following calculation formula e1,are produced for the input bits d1 and d0 of the additional errorcorrection encoder 110.L(00)∝_Log P(d1d0=00|observation)L(01)∝_Log P(d1d0=01|observation)L(10)∝_Log P(d1d0=10|observation)L(11)∝_Log P(d1d0=11|observation)  (e1)

The soft outputs produced by the SSA decoder are measurements of theprobability values for four kinds of combinations of “d1” and “d0”attained after the decoding. Meanwhile, when a convolutional code as anexternal code is used, these soft outputs are directly used as thebranch metric.

Successively, the ATSC and additional data of the soft signal formoutputted from the TCM decoder 230 are deinterleaved in thedeinterleaver 240.

In this case, the ATSC data, which are outputted from the deinterleaver240 are made random in the randomizer 130 of the transmitter, come topass through the derandomizer 280. Besides, as the derandomizer 280needs a hard signal form, hard decision should be carried out on theATSC data outputted from the deinterleaver 240 as the soft form.

Yet, the hard decision process is unnecessary for the additional data,which are outputted from the deinterleaver 240 and fail to pass throughthe derandomizer 280.

Therefore, in order to carry out the hard decision process on the ATSCdata outputted from the deinterleaver 240, the ATSC data pass throughthe limiter 260 and the RS decoder 270 in order and then are inputted tothe derandomizer 280.

However, in order to remove the parity added thereto in the transmitterwithout the hard decision process, the additional data outputted fromthe deinterleaver 240 pass through the RS parity removal part 290 andthen go by way of the additional error correction decoder part 300.

As mentioned in the above description, the digital communication systemaccording to the present invention enables to carry out a datatransmission of a high reliance having a signal to noise ratio by addingan additional error correction encoder having a desirable statetransition property when used with the mapping of the TCM encoder to anoutside of the TCM encoder, thereby enabling to improve a performance ofthe digital communication system.

The forgoing embodiments are merely exemplary and are not to beconstrued as limiting the present invention. The present teachings canbe readily applied to other types of apparatuses. The description of thepresent invention is intended to be illustrative, and not to limit thescope of the claims. Many alternatives, modifications, and variationswill be apparent to those skilled in the art.

1. A Vestigial Sideband (VSB) transmitter for transmitting a terrestrialbroadcasting signal including main Advanced Television Systems Committee(ATSC) data and enhanced supplemental data, the VSB transmittercomprising: an additional error correction encoder for encoding theenhanced supplemental data for error correction; a multiplexer formultiplexing the encoded supplemental data and the main ATSC data; aTrellis Coded Modulation (TCM) encoder for encoding or bypassing a firstinput data bit in accordance with whether the first input data bitbelongs to the main ATSC data or the enhanced supplemental data and fortrellis-encoding a second input data bit, wherein the first and seconddata bits are generated based on the multiplexed data; and a VSBmodulator for modulating a signal generated based on the data bitsoutput from the TCM encoder and transmitting the modulated signal to oneor more VSB receivers.
 2. The VSB transmitter of claim 1, furthercomprising: a randomizer for randomizing the multiplexed data; aReed-Solomon coder for coding the randomized data; and an interleaverfor interleaving the Reed-Solomon coded data and outputting theinterleaved data into the TCM encoder.
 3. The VSB transmitter of claim2, wherein the randomizer processes the ATSC data only.
 4. The VSBtransmitter of claim 1, wherein the additional error correction encoderis designed in accordance with signal mapping of the TCM encoder.
 5. TheVSB transmitter of claim 1, wherein the additional error correctionencoder uses a convolutional encoding method.
 6. The VSB transmitter ofclaim 1, wherein the TCM encoder comprises: a first coder for coding thefirst input data bit and outputting the coded first input data bit if itbelongs to the main ATSC data, the first coder directly outputting thefirst input data bit without coding if it belongs to the enhancedsupplemental data; a second coder for coding the second input data bit;and a VSB mapper for mapping the coded or uncoded first input data bitoutputted from the first coder and the coded second input data bit intoa corresponding signal.
 7. A Vestigial Sideband (VSB) transmitter fortransmitting a terrestrial broadcasting signal including main AdvancedTelevision Systems Committee (ATSC) data and additional data, the VSBtransmitter comprising: an additional error correction encoder forperforming state transition processes on the additional data; a mainprocessor for operating in accordance with the state transitionprocesses of the additional error correction encoder and configured tochange input data if it belongs to the main ATSC data, and to bypass theinput data if it belongs to the additional data; and a VSB mapper formapping the coded or uncoded input data outputted from the mainprocessor into a corresponding signal.
 8. The VSB transmitter of claim7, further comprising a multiplexer for multiplexing the main ATSC dataand the additional data outputted from the additional error correctionencoder, and outputting the multiplexed data to the main processor. 9.The VSB transmitter of claim 8, further comprising: a randomizer forrandomizing the multiplexed data; a Reed-Solomon coder for coding therandomized data; and an interleaver for interleaving the Reed-Solomoncoded data and outputting the interleaved data into the main processor.10. The VSB transmitter of claim 9, wherein the randomizer processes theATSC data only.
 11. The VSB transmitter of claim 7, wherein theadditional error correction encoder is designed in accordance with asignal mapping of the main processor.
 12. The VSB transmitter of claim7, wherein the additional error correction encoder uses a convolutionalencoding method.
 13. The VSB transmitter of claim 7, wherein the mainprocessor comprises: a processor for changing a first data bit of theinput data and outputting the coded first data bit if it belongs to themain ATSC data, the processor directly outputting the first data bitwithout changing if it belongs to the additional data; and a coder forcoding a second data bit of the input data.
 14. The VSB transmitter ofclaim 7, further comprising a data format converter for formatting thesignal output from the VSB mapper and transmitting the formatted data toone or more VSB receivers.
 15. The VSB transmitter of claim 14, whereinthe data format converter comprises: a synchronizing multiplexer formultiplexing the signal outputted from the VSB mapper with a fieldsynchronizing signal and segment synchronizing signals; a pilot inserterfor inserting pilot signals into the multiplexed signal; a modulator formodulating the pilot-signals-inserted signal into an intermediatefrequency (IF) signal; and a Radio Frequency (RF) converter forconverting the modulated signal into a Radio Frequency (RF) signal fortransmission.
 16. A digital television (DTV) receiver for processing adigital broadcast signal generated from encoding additional input datafor additional error correction, multiplexing the encoded additionalinput data with conventional input data, Reed-Solomon (RS) encoding themultiplexed input data, interleaving the RS-encoded data, performingTrellis Coded Modulation (TCM) encoding on the interleaved data, andtransmitting a Radio Frequency (RF) digital broadcast signal includingthe TCM-encoded data, the DTV receiver comprising: a tuner for receivingthe RF digital broadcast signal containing first service datacorresponding to the conventional input data and second service datacorresponding to the additional input data; a demodulator fordemodulating the broadcast signal; a TCM decoder for performing trellisdecoding on the first and second service data in the demodulatedbroadcast signal for first error correction in order to correct errorsin the first and second service data that occurred during reception ofthe broadcast signal, and for outputting the first and second servicedata as a soft signal; and an additional error correction decoder fordecoding the trellis-decoded second service data for second errorcorrection in order to additionally correct errors in the second servicedata that occurred during the reception of the broadcast signal.
 17. TheDTV receiver of claim 16, wherein the first service data compriseAdvanced Television Systems Committee (ATSC) data.
 18. The DTV receiverof claim 16, wherein the TCM decoder uses one of MAP (Maximum Aposteriori Probability) and SOVA (Soft-Out Viterbi Algorithm) in orderto output the first and second service data as a soft signal.
 19. Amethod of processing a digital broadcast signal generated fromadditional error correction encoding additional input data, multiplexingthe encoded additional input data with conventional input data,Reed-Solomon (RS) encoding the multiplexed input data, interleaving theRS-encoded data, performing Trellis Coded Modulation (TCM) encoding onthe interleaved data, and transmitting a Radio Frequency (RF) digitalbroadcast signal including the TCM-encoded data, the method comprising:receiving, through a digital television (DTV) receiver, the RF digitalbroadcast signal containing first service data corresponding to theconventional input data and second service data corresponding to theadditional input data; demodulating the received RF digital broadcastsignal; performing trellis decoding on the first and second service datain the demodulated broadcast signal for first error correction in orderto correct errors in the first and second service data that occurredduring reception of the broadcast signal; outputting the first andsecond service data as a soft signal; and decoding the trellis-decodedsecond service data for second error correction in order to additionallycorrect errors in the second service data that occurred during thereception of the broadcast signal.
 20. The method of claim 19, whereinthe first service data comprise Advanced Television Systems Committee(ATSC) data.
 21. The method of claim 19, wherein the first and secondservice data are output as a soft signal using one of MAP (Maximum Aposteriori Probability) and SOVA (Soft-Out Viterbi Algorithm).
 22. Amethod of processing a digital broadcast signal generated fromadditional error correction encoding additional input data, multiplexingthe encoded additional input data with conventional input data,Reed-Solomon (RS) encoding the multiplexed input data, interleaving theRS-encoded data, performing Trellis Coded Modulation (TCM) encoding onthe interleaved data, and transmitting a Radio Frequency (RF) digitalbroadcast signal including the TCM-encoded data, the method comprising:receiving, a digital television (DTV) receiver, the RF digital broadcastsignal containing first service data corresponding to the conventionalinput data and second service data corresponding to the additional inputdata; demodulating at least one of the first service data and secondservice data included in the received RF digital broadcast signal;performing trellis decoding on the second service data in thedemodulated broadcast signal for first error correction in order tocorrect errors in the second service data that occurred during receptionof the broadcast signal; outputting the second service data as a softsignal form; and decoding the trellis-decoded second service data forsecond error correction in order to additionally correct errors in thesecond service data that occurred during the reception of the broadcastsignal.
 23. The method of claim 22, wherein the first service datacomprise Advanced Television Systems Committee (ATSC) data.
 24. Themethod of claim 22, wherein the first and second service data are outputas a soft signal using one of MAP (Maximum A posteriori Probability) andSOVA (Soft-Out Viterbi Algorithm).